Tempest by Julie Cross
First chapters revealed from romantic time-travel thriller ‘Tempest’
Click here for a link to the first four chapters of the book, which comes out in its entirety Jan. 3, 2012. 
Jackson Meyer, a charming, somewhat reckless, young man is as baffled by his ability to become unstuck in time as anyone, though it’s largely a secret between him and a physics expert friend named Adam. As the story begins, we see Jackson and girlfriend Holly working as camp counselors during a youth-group visit to the zoo, though Jackson is preoccupied by efforts to test his power.
The theory: though he can shift backward in time (usually by only 30 minutes or so) nothing he changes in the past actually shows up when he returns to the present.
That raises all sorts of questions about the story. Is he really time traveling? Adam describes him going into a vegetative state during his backward jaunts, so could the past Jackson sees really be hallucinations or dreams? Or is he splitting off alternate timelines when he shifts back, nature’s way of avoiding the paradoxes that would inevitably arise due to changing the past?